Conventionally, in the above-mentioned machine tool such as a lathe, when switching tools used in machining, for example, there is employed such a tool switching method as shown in FIGS. 17A to 17D and 18. That is, in this machine tool, a tool post 61, on which there are parallel arranged tools 62A, 62B and 62C respectively composed of cutting tools or the like, can be moved correspondingly to a work W not only along the X axis direction which is the advancing and retreating direction of the tools 62A to 62C but also along the Y axis direction which is the parallel arranged direction of the tools 62A to 62C. And, for example, after end of machining of the work W using the tool 62A, when switching the tool 62A over to the tool 62C while skipping the tool 62B with its tool nose projecting, firstly, as shown in FIG. 17A, the tool post 61 is positioned at a first position P1 where the nose of the tool 62A has a given clearance C with respect to the outer peripheral surface of the work W.
After then, as shown in FIG. 17B, the tool post 61 is moved in the X axis direction and is positioned at a second position P2 where the nose of the tool 62B to be skipped has the given clearance C with respect to the outer peripheral surface of the work W. This second position P2 is a transit position where, when the tool post 61 is moved in the Y axis direction, interference between the most projecting tool 62B and work W can be avoided. Next, as shown in FIG. 17C, the tool post 61 is moved in the Y axis direction while skipping the tool 62B and is positioned at a third position P3 where the nose of the tool 62C exists on an X-axis direction extended line passing through the center of the work W. Further, as shown in FIG. 17D, the tool post 61 is moved forward in the X axis direction and is positioned at a fourth position P4 where the nose of the tool 62C has the given clearance C with respect to the outer peripheral surface of the work W.
However, in the conventional movement control method, there is found a problem that, since the tool post 61, at the second position P2 and third position P3, is switched in the moving direction while it is stopped between the X and Y axis directions, the moving time of the tool post 61 in the tool switching operation is long. That is, as shown in FIGS. 18 and 19, where the moving time between the first position P1 and second position P2 is expressed as t1, the moving time between the second position P2 and third position P3 is expressed as t2, and the moving time between the third position P3 and fourth position P4 is expressed as t3, the moving time t0 necessary for the tool replacement is at least t1+t2+t3.
On the other hand, in JP-A-9-262742, there is disclosed a tool movement control method in which, a tool is moved overlappingly in two axes directions in a given time zone to thereby shorten the tool moving time. Also, in JP-A-11-104934, there is disclosed a tool movement control method in which when replacing a tool, while the tool is being moved from the current position to a tool replacement position, there is set an approach position for allowing the tool to pass while avoiding interference with other parts and, at the approach position, the tool is moved overlappingly without stopping the rapid traverse movements in two directions, thereby shortening the tool moving time. Further, in JP-A-2006-24174, there is disclosed a moving member movement control method in which a moving member is moved at a rapid traverse speed by a first axis drive device up to a direction switching point for avoiding interference with other parts, and the moving member is slowly moved at an accelerating or decelerating speed equal to or lower than the maximum accelerating or decelerating speed of the first axis drive device within the moving time of the second axis drive device after the moving member arrives at the direction switching point, thereby shortening the moving time of the moving member.